On 20 Nov 2011, at 17:27, Jason Resch wrote:

Hi Bruno,

I had few questions regarding some of the things said in your post.

On Sat, Nov 19, 2011 at 3:49 AM, Bruno Marchal <marc...@ulb.ac.be> wrote:

On 19 Nov 2011, at 03:02, Pierz wrote:

David Deutsch's idea
of a good explanation is one that closely matches the structure of the
thing it describes, allowing for little variation. The vast variation
in the possible worlds where UDA could be invoked makes it a bad
explanation, in those terms.

You have just not (yet) understood the role of the 1/3 person pov distinction in the reasoning. UDA shows that physics is determined by a relative measure on computations. If this leads to predict that electron weight one ton then mechanism is disproved. UDA shows that physics is entirely reduce to computer science/number theory in a very specific and unique way (modulo a variation on the arithmetical definition of knowledge).





Couldn't the UD predict various computational histories and different types laws of physics for different observers?

I don't think so, because physics is given by ALL computations going through your state, and that means any state accessible by a universal numbers/machines. The "different observers" and "other universes" have to be too much different. They cannot be Turing universal. If they are, you appear in their computations, and so become part of your physics. I will reexplain this to Stephen and Johnathan, so don't worry if this is not clear.



Of course the electron weighing a ton might be ruled out from observation if such electrons are incompatible with life, but I don't see that the UD could ever perfectly derive the laws of physics if there are multiple computational histories compatible with observers.

By UDA, physics is neither a computation, nor the result of a computation. It is the result of interference of all (relative) computations. The computation leading to non universal observers have a measure null with respect to the "real (arithmetical) measure". They exist in UD*, but does not influence what we observe. They are "white rabbit computations".







For example, might there be such histories that have observers but no electrons at all? I see the UD perhaps being used in the future to derive a rough estimate of the probabilities for different common universes observers might expect to find themselves in, but nothing definite.

This is not entirely excluded, but then the mass or the existence of electron is a geographical phenomenon.








This is not a problem for an Everett -type multiverse, in which the
universes are bound together by consistent physical laws which allow
one to speak of a proportion of universes in which event x occurs.
However, in a mathematical platonia where all possible calculations
occur, and nothing outside of them, there can be no such ordering
principle.

If the Everett idea works, and is the solution, (which has not yet been completely proved) then the UDA conclusion is that the Everett simultion in the UD wins the "measure battle", and we HAVE to justify this from computer science alone.



More general physical principals like the Schrodinger equation might be applicable to all observers if it is truly, as Russell staid, a theory of observation. But something like the weight of the electron, the Gravitational constant are, in my mind, more properly considered local properties rather than global principals.

This is possible. It would make the mass of the electron similar to the mass of the planet around the sun, that is: a geographical contingent reality, as unpredictable than being myself in W or in M after a self-duplication. The advantage of comp is that it gives what is really invariant for all universal numbers, in any lawful and persistent (from its point of view) environments.

More on this later.

Bruno


http://iridia.ulb.ac.be/~marchal/



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